Simulation Of Radial Expanding To Release Stresses For Large-Diameter Straight-Weld Pipe

Pipeline structures are widely used in the vital departments of the national economy, such as oil industries, chemical industries and the city planning constructions. Especially recent years,"transporting natural gas from west to east"had been started, that would push our pipeline industries to a new developing tide. In the molding and welding process of pipelines, it will inevitably produce the molding residual stresses and the welding residual stresses. These residual stresses and deformation will cause badly influence for intension and properties of pipeline, so after the welding process, the next step is the second molding of pipeline-expanding, that can reduce or release residual stresses of welding pipe and make it better, expanding is an important technique of pipeline molding.This paper mainly research the effect of expanding technique to release residual stresses for pipeline. On the basis of elastic-plastic large deformation theory and thermal-elastic-plastic theory, using the ANSYS non-liner finite element program to simulate three technics processes(including moulding process, welding process and expanding process) for X70 large-diameter straight-weld pipe. The paper covers the following aspects concerning the main work and research in the project.First, a three-dimensional finite-element model of straight-weld pipe is founded. On the basis of elastic-plastic large deformation theory, contact-friction theory, thermal-elastic-plastic theory and springback theory, for the first time to simulate the whole process for straight-weld pipe, obtain the stress fields of molding and welding and the residual stress distributions. On the basis of above results, going on expanding simulation.We obtain the stress-strain field and residual stress distribution after expanding.Second, simulating the expanding process of different expanding ratioes ( 0.8%,1.0%,1.2% and 1.4%) for the straight-weld pipe with mould residual stress and weld residual stress. On the different ratios, residual stresses of weld-pipe are obtained. Analysis the fore-and-aft change of residual stresses for expanding and the different effect for releasing residual stresses.The result of study show that expanding technique have good effects on reducing and releasling residual stresses that caused in the process of molding and welding. After reasonable expanding, peak value of residual stresses on the seam and the...